Typical operating systems (e.g., windows-based systems by Microsoft, Sun Solaris™, Linux™, MacOS by Apple Computer, Unix, etc.) provide a resource manager. The resource manager shares the resources of a computer system with the applications requesting use of the resources. Typical resources that are managed by a resource manager include processors, disk space, memory, peripheral devices, etc. For example, if two applications request to use the printer, the resource manager determines which application uses the printer first by placing requests into a queue.
In a distributed system, computer systems may be located in multiple locations throughout a private or public network. The computer systems within a distributed system may be considered a client, a server, or act as a client and server in certain situations. The client is typically the computer system that requests a service or resource, while the server is a computer system that shares a resource or performs a service (hereinafter, the use of the term “resource” is intended to refer to resources or services). A distributed system is useful because the distributed system allows the load created from the client requests to be distributed among a number of servers, thereby increasing the throughput of the entire system by leveraging the underutilized resources in the distributed system.
The resources that a server provides may range from processor time to storage space. In a distributed system, a client may request a resource, and the request is serviced by one of the number of servers with the resource available. Further, using a distributed system allows several requests to be handled simultaneously. Allowing the load to be distributed among a plurality of servers may help reduce the load placed on an individual server (whether on the processor, storage system, etc.).
Several methods are currently used to provide the location of a server where the requested resource may be found. These methods include using directory services, broadcasting, and querying (e.g., unicast, multicast, etc.). The current methods may provide a one-to-one mapping of a client and a server that handles the request of the client. With this method, several servers may be available to satisfy requests, but individual clients are mapped directly to specific servers. Another method, for example, may send a request out to the network, where servers that are listening for requests respond.
As discussed above, the server may handle a client's request for a resource using a one-to-one mapping. For example, a client, Client X, may have an object, Object A, that needs to be stored. Client X may be mapped, using a one-to-one mapping, with Server Z. In this distributed system, Client X may send a request to Server Z to store Object A. Several possibilities may occur. Server Z may reply indicating that space is available and Object A may be stored on Server Z. Server Z may reply indicating that space is not available, and Object A cannot be stored on Server Z. Server Z may reply indicating that the Server Z is busy, and the request is handled later. Server Z may not reply. In this type of system, the server typically is prepared for the specific types of requests that a client may make, and has a large amount of resource available.
In a distributed system, a distributed hash table (DHT) may be used to store and locate data throughout the number of servers. No central server is required to locate the data, instead each server has a partial list that may be used to determine where the data is located in a short series of steps. DHT allows the use of a programming interface with services that may be used to store data, distribute data, etc. DHT provides an algorithm to locate data once the data is stored in one of the number of servers. DHT treats each server like a bucket in a hash table, and assigns the responsibility of data to a server using a hash function allowing easy lookup when the data is needed.